1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming a gate electrode having a stacked structure of a polysilicon layer and a refractory metal layer in a semiconductor device.
2. Description of the Related Art
Since a gate resistivity is important factor in the manufacture of highly integration of semiconductor device, the gate electrode is formed to a stacked structure of a polysilicon layer and a refractory metal, for reducing the gate resistivity. A tungsten(W) layer is used as the refractory metal. A barrier metal layer is also interposed between the polysilicon layer and the tungsten layer to prevent diffusion therebetween. The barrier metal layer is formed of a titanium nitride(TiN) layer or a tungsten nitride(WN) layer. Furthermore, for removing damage and residues due to the etching process and recovering the reliability of a gate oxide layer after forming the above gate electrode, gate re-oxidation process is performed.
In the gate re-oxidation process, however, the volume of the tungsten layer expands due to its fast oxidation rate, so that the morphology of the gate electrode is transformed. Therefore, it is difficult to perform ion-implantation for forming a source and a drain. Furthermore, gate resistivity increases.
To overcome the above problems, as the gate re-oxidation process, a selective oxidation process which oxidize selectively the only polysilicon layer, is suggested. However, since the selective oxidation process is performed at the high temperature, there is another problem that thermal budget occurs.